Copending application Ser. No. 760,339 and application Ser. No. 604,845, now U.S. Pat. No. 4,642,682, the disclosures of which are incorporated herein by reference and made a part hereof, disclose a phase responsive color video signal correction system which allows correction of the spectral distribution and luminance aspects of a phase-encoded composite video signal. U.S. Pat. No. 4,096,523 to Belmares-Sarabia, the disclosure of which is incorporated herein by reference and made a part hereof, discloses another technique for color correcting video signals wherein the primary color video signals are separated into six independent primary and complementary video signals over which separate control can be exercised in making color corrections. The latter system is sometimes known as a "six vector" or "multi-vector" system.
While both of the above-referenced video signal control systems allow color correction of input video signals, both systems leave room for advancement in selecting a portion of an image represented by an input video signal for correction. Most color correction systems are generally hue oriented, in that the controls over video parameters such as hue, saturation, and luminance are grouped or organized according to hue. For example, in the Belmares-Sarabia system a panel of hue, saturation, and luminance controls is provided, there being a separate hue, saturation, and luminance control for each one of the six primary and complementary colors. In the referenced copending phase responsive video signal control system, there is also a separate hue, saturation, and luminance control for each of the color vectors or fans. Both these systems may be considered a "control per hue" system.
While there is greater selectivity in the phase responsive system which allows an operator to select a hue for correction with greater particularity, the increased number of controls available to the operator which results from greater selectivity sometimes leads to confusion in selection of a color for control. Operators of control correction systems invariably must observe the video scene to be corrected on a color monitor, and observe variations in the image as various controls are moved until the image is aesthetically satisfactory. The proliferation of possible control provided in the copending phase responsive composite video signal control system requires an operator to constantly shift his attention between the image on the video monitor and the control panel to ensure that the proper control is moved and that settings previously made to other portions of the video image are not disturbed. Upon viewing an image which includes a region whose colorimetry is unsatisfactory, the operator must mentally associate the hue of the unsatisfactory region with the set of controls having the most pronounced influence on the region. This leads to possible inefficiencies in operation and slows the color correction process. The more controls there are, i.e. the more hues over which control may be selectively exercised, the more difficult is the task of selecting the proper set.
Accordingly, there is a need for color video control circuitry which is able to select a portion of a video image for colorimetry correction without requiring an operator to mentally associate a particular hue with a particular set of controls.